1. Field of the Invention
This invention relates to integrated circuit structures constructed on semiconductor substrates. More particularly, this invention relates to a process for treating damaged surfaces in low dielectric constant organo silicon oxide insulation material to inhibit moisture absorption by such damaged low dielectric constant insulation material.
2. Description of the Related Art
In the construction of integrated circuit structures, dielectric materials such as silicon oxide (SiO.sub.2) have been conventionally used to electrically separate and isolate or insulate conductive elements of the integrated circuit structure from one another. However, as the spacing between such conductive elements in the integrated circuit structure have become smaller and smaller, the capacitance between such conductive elements through the silicon oxide dielectric has become of increasing concern. Such capacitance has a negative influence on the overall performance of the integrated circuit structure in a number of ways, including its effect on speed of the circuitry and cross-coupling (crosstalk) between adjacent conductive elements.
Because of this ever increasing problem of capacitance between adjacent conductive elements separated by silicon oxide insulation, as the scale of integrated circuit structures continues to reduce, the use of other insulation materials having lower dielectric constants than conventional silicon oxide (SiO.sub.2) has been proposed. One such material is a methyl silicon oxide material wherein at least a portion of the oxygen atoms bonded to the silicon atoms are replaced by methyl (CH.sub.3 --) groups. Such a methyl silicon oxide dielectric material has a dielectric constant of about 2.9 and is, therefore, of great interest as a low dielectric constant substitute for the conventional silicon oxide (SiO.sub.2) insulation material.
While the substitution of one or more methyl groups for some of the oxygen atoms bonded to the silicon atoms has a beneficial effect in the lowering of the dielectric constant of the organo silicon oxide material, therefore lowering the capacitance between conductive elements separated by such dielectric material, it has been found that the bond formed between the silicon atoms and the methyl group is not as stable as the silicon-oxygen bond found in conventional silicon oxide (SiO.sub.2) materials.
In particular, for example, when the surface of such a low dielectric constant methyl silicon oxide insulation layer is exposed to oxidizing or "ashing" systems, which are used to remove a photoresist mask from the low dielectric constant methyl silicon oxide insulation layer, after formation of openings therein, it has been found that the ashing process results in damage to the bonds (severance) between the methyl radicals and the silicon atoms adjacent the surfaces of the low dielectric constant methyl silicon oxide insulation layer exposed to such an ashing treatment. The term "openings", as used herein, is intended to describe either vias between two layers of metal interconnects or contact openings between devices on the substrate and a metal interconnect layer. This severance of the carbon-silicon bonds, in turn, results in removal of such organic materials formerly bonded to the silicon atoms along with the organic photoresist materials being removed from the integrated circuit structure. The silicon atoms from which the methyl radicals have been severed, and which are left in the damaged surface of the low dielectric constant methyl silicon oxide insulation layer, have dangling bonds which are very reactive and become water absorption sites if and when the damaged surface is exposed to moisture. The damaged low dielectric constant methyl silicon oxide insulation layer, and its resultant susceptibility to moisture may be illustrated by the following equations: ##STR1##
This absorption of moisture by the damaged low dielectric constant methyl silicon oxide insulation material, results in hydroxyl bonding to the dangling silicon bonds left from the severance of the carbon-silicon bonds in the damaged surface of the low dielectric constant methyl silicon oxide insulation layer. This silicon-hydroxyl bond is not a stable bond and subsequent exposure to heat, e.g., during subsequent processing such as annealing, can result in severance of the silicon-hydroxyl bond, thereby causing water vapor formation which, for example, can interfere with subsequent filling of a via/contact opening or a damacene trench with metal filler material. It would, therefore, be desirable to repair any damage done to the low dielectric constant methyl silicon oxide insulation layer by the severance of the carbon-silicon bonds prior to any exposure of the damaged surface to moisture to thereby ensure against formation of unstable silicon-hydroxyl bonds in the damaged surface of the low dielectric constant methyl silicon oxide insulation layer.